Project Summary/Abstract Emotion reactivity, self-regulation, and effortful control are increasingly recognized as core disruptions in attention-deficit/hyperactivity disorder (ADHD). This study logically follows prior work of PI Musser, co-I Nigg, and colleagues, as well as others in the field, who have begun to examine the roles of these cognitive and emotion factors in ADHD. In prior samples, it has been demonstrated that: 1) ADHD is associated with disruptions in emotional reactivity and regulation (i.e., behavioral and biological), 2) behavioral individual differences observed in ADHD (e.g., surgency, irritability) are explained in part by differential patterns of behavioral and biological emotional reactivity and regulation, 3) cognitive heterogeneity observed in ADHD (e.g., working memory deficits) is explained in part by disruptions in regulation, and 4) ADHD is associated with disruptions in biological and behavioral reward/punishment sensitivity. Thus, theoretical frameworks describing roles of emotion reactivity and both implicit and explicitly regulatory processes as multiple pathways in the expression of ADHD have been supported by this work. Replication of these effects in additional samples is needed to better understand the nature of these associations. Additionally, the degree to which these cognitive and emotion factors may explain individual differences in treatment response in ADHD by serving as potential as mechanisms of change in response to stimulant medications has yet to be investigated. Understanding cognitive and emotional factors' roles in treatment response has the potential to both inform clinical practice and broader ADHD etiological theory. This study takes advantage of co-I Pelham's Tolerance Study (R01 MH00990303-01), a double-blind, cross-over design examining stimulant medication (OROS Methylphenidate) tolerance in children with ADHD. 240 ADHD children will undergo an intake procedure to enter the 8 week Summer Treatment Program (STP). During the first two weeks of the STP, OROS will be titrated to an optimal dose for each child. Children will be randomly assigned: placebo (n=120) or ORSO (n=120) for three weeks. Children will be placed in the cross-over condition for an additional 3 weeks. The proposed study will ask enrolled participants of the Tolerance Study, as well as 120 community-recruited controls to complete a protocol examining the roles of emotion reactivity, self-regulation, and effortful control in 1) heterogeneity in ADHD behavioral profiles, 2) heterogeneity in ADHD treatment response, and 3) mechanisms of change underlying response to stimulant medications. All participants (both ADHD and controls) will complete the task battery for the proposed study, including an emotion induction and suppression, emotional go/no-go, standard go/no-go, spatial span, and reward delay, while psychophysiological data are collected via electrocardiogram, impedance cardiogram, and electrodermal activity. This research will be of interest to researchers with in the field of ADHD etiology and treatment, as well as to practitioners interested in improving treatment response.